Ethanol or methanol is a combustible liquid and, when treated to have a higher concentration, it is increased in combustion energy. Thus, it can become an alternative fuel to gasoline, light oil or the like which is used in an internal combustion engine, etc. In recent years, moreover, moves to utilize alcohol fuels as fuels for automobiles, etc. have been speeded up, because of the limited amounts of fossil resources such as gasoline, light oil, and kerosene, and because of environmental problems. In this case as well, high concentration ethanol, for example, is needed.
As a method for concentrating ethanol, a distillation method is generally known. With this method, however, a huge amount of energy is required for heating, pressurization, etc.
As methods for concentrating ethanol at low costs, moreover, proposals have been made for an alcohol concentration method utilizing a supercritical state (Patent Document 1), and a polymer membrane separation process (Patent Document 2).
A disclosure is also made of a method which comprises reacting an alcohol in an alcohol-containing aqueous solution with a predetermined fatty acid to convert the alcohol into a hydrophobic ester compound, and hydrolyzing the hydrophobic ester compound to obtain ethanol (Patent Document 3).